1. Field of the Invention
This invention relates to an image forming system.
2. Description of the Related Art
Conventionally, double-side printing by using an image forming apparatus is performed by printing one side of a sheet of paper in an image forming unit and thereafter, conveying the sheet of paper to the image forming unit again to print the other side of the paper. Because of this, productivity is halved in the double-side printing compared to that in single-side printing.
Accordingly, in order to improve the productivity of the double-side printing, an image forming system of a tandem configuration is known, in which a plurality of image forming apparatuses are connected in series along a paper conveying direction, the image forming apparatus provided on the upstream side (upstream device) prints a front side of the paper, and the image forming apparatus provided on the downstream side (downstream device) prints a reverse side of the paper.
For example, a technique is proposed in a system in which two printers are connected in series, in which each of the printers informs the other of error information by serial communication to thereby share the error information (Refer to Japanese Unexamined Patent Application Publication No. 2009-298009). By utilizing the serial communication, the increase in cost caused by adding signal lines between the printers is prevented.
However, in a case of configuring an image forming system of a tandem configuration in which each apparatus developed as a stand-alone image forming apparatus is connected to the other in series, each image forming apparatus cannot recognize a paper feed tray which is not directly connected to the own apparatus. Therefore, if a job includes an instruction accompanying an operation of the paper feed tray which is not directly connected to the own apparatus, the job is determined not executable at each image forming apparatus and error occurs, even if the job is executable in the system.
Further, operations become complicated in each image forming apparatus, to process the job to prevent errors caused by presence of the paper feed tray not directly connected to the own apparatus and to individually change a control program of each image forming apparatus suitable for the tandem configuration.